Metal alloy resistors



April 26, 1966 c. GANCI METAL ALLOY RESISTORS Filed Dec. ll, 1962 IN VENTOR. f/S & a/757' BY United States Patent O Filed Dec. 11, 1962, Ser. No. %3,883 3 Claims. (Cl. 338-264 This invention relates to electrical resistors and particularly to the composition of the metal alloy forming the element.

The invention is particularly directed to electrical resistors with wound resistive elements on a ceramic base and covered by a vitreous enamel coating. For good thermal and physical shock qualities, the base of the resistor should have a low coefiicient of expansion and the coefficient of expansion of the coating should be slightly lower than that of the base. For high quality, high precision, reliable resistors it -is also desirable that the resistance' element have certain characteristics and meet certain standards.

Some of theeare that the temperature coefi'icient of resistance should be zero or nearly zero so that the resistor may be subjected to-high temperatures in operation without' a material or, if possible, any change in resistance value of the resistive element due to temperature rise; and that the alloy should have a .ductility and high tensile strength in order to form fine, strong wire or ribbon. The resistance value of the element should remain substantially constant over sustained periods of high heats so as to have a stable electrical load life.

A particularly desirable feature is to have the low coefficient of expansion of the base and the linear coefficient of thermal expansi-on of the element approximately the same. Heretofore the coefficients of expansion of the resistive elements have been approximately twice that of the base. The coefficent of expansion of the base has been 6 to 9)( 10- inches per inch per degree centigrade, while that of the resistive elements has been 15 to 18 10 i inches per inch per degree centigrade.

When the coefficient of expansion of the wire issubstantially greater than the coeflicient of expansion of the base, difficulties are encountered during the formation of the protective coating. The resistor is subjected to high temperatures, the wire expands and loosens which causes the wires to pull, bunch or swim, possibly causing shorting of the turns which may result in rejections for resistance values creating hot spots and resulting in un reliability.

Also, the different and lower coefficient of expansion of the coating further aggravates these difficulties.

An object of this invention is to provide an electrical resistor having a base with a low coefficient of expansion and a resistive element of substantially the same coeflicient of expansion as the base.

Another object of the invention is to provide a resistance element that has a low temperature coeificient of resistivity and a comparatively low temperature coefiicent of expansion that `is ductile and has a high tensile strength.

Other and further objects will be apparent from the description taken in connection with the drawings, in which FIG. 1 illustrates a wire wound tubular resistor with tab type terminals;

FIG. 2 illustrates a wire. wound tubular resistor with axial leads; i

FIG. 3 illustrates a plaque type of resistor;

FIG. 4 illustrates a strip type of resistor;

FIG. 5 illustrates a disc type of resistor; and

FIG. 6 illustrates a tubular base with a crinkled ribbon per inch per degree centigrade.

shape and the resistance wire is helically wound on the base and soldered or welded to the terminals 11 and 12. A coating 14 may encase the wire and terminal to protect the wire from physical injury and corrosion. A vitreous enamel coating is illustrated, but other types of coatings, such as cements, Teflon, silicone and the like, may be used depending upon the particular characteristics desired.

The base 10 may be composed of various types of ceramics, such as steatite, alumina, modified talc, fosterite compositions, zircon compositions and other known ceramics. The linear coeflicient of thermal expansion of steatite is 7 10- fto 8.5Xl0 fosterite is 10 to 10.5 10- orless, zircon is 5 to 7.5 10 and alumna is 7 to 8.5 10- inches per inch per degree centigrade. Illustrative compositions of these ceramics are set forth as follows:

The metal of the terminals 11 and 12 has a coeflicient` of expansion approximately the same as the ceramic base 10 and may be an alloy, such as a nickel-iron alloy having a range of coefcients from very low to 16 10- inches Alloys having coeflicients of expansion in the range of 6 to 10 10 are selected to match the coefficients of expansion of the foregoir'g ceramic bases. 'Thus the terminals will have substantially the same or the same coeflicient of expansion as the base.

The particular resistive element of this invention comprises a titanium alloy including vanadium and aluminum. Various compositions are set forth as follows:

approximately 9.5 to 10 10- inches per inch per degree centigrade. These alloys have a specific resistance of about 900 ohms per circular mil foot and a 'temperature coeficient of resistivity of less than parts per million. The alloys have good ductility and tensile strength and may be formed into small diameter wires or thin ribbons. The wires are easily wound on the base in conventonal manner and Secured to the base by conventional means, such as welding.

Various types of well-known coatings may be used to encase the resistive element and terminals as illustrated. Vitreous enamel coatings should have coefficients of expansion less than the coefiicients of expansion of the base material in order to avoid crazing of the ena-mel. The coeflicients of expansion are in the range of 5 to 9)( IO- inches per inch per degree centigrade. Cement, plastc and other types of coatings may be used.

In FIG. 2 the invention is illustrated in connection With an axial type of resistor having end cap 16 mounted on the base with the axial leads 18. In FIG. 3 the wire element is wound in a non-inductve manner on a plague type of base fragmentarily shown. The wire element 19 is formed on the posts 20 and embedded in a vitreous enamel or cement coatng. In FIG. 4 a resistor With an elliptical 'base 21 is partially illustrated With the tab type of terminal 22 and a wire wound resistive element 23. A vitreous enamel coating is illustrated at 24. FIG. 5 illustrates a radial type of resistor With the resistive element 25 intertwined in bosses 26.

In 'FIG. 6 a tubular base resistor is illustrated with a crinkled ribbon type of resistive element 27 formed on the base 28 and attached to terminals 29. In referrng to a wire type of resistive element, the ribbon form is in cluded in the meaning of this term. The titanium alloy forms a tough ribbon wire which retains its shape and is easily wound on the base.

A preferred form of the base to match coefficients of expansion of the base and the resistance element is a beryllium oxide base of 99 to 100% beryllium oxide. This produces ,an electrical resistor of greater reliability and higher wattage for a given size. The beryllium oxide base has a very good heat conductivity for conducting the heat of the resistive element.

In addition to the resistive element and the base having substantially the same coefficent of expansion, the terminals -may be also made of the metal alloy that has a coefiicent of expansion substantially equal to that of the base. The coatings may be any of the well-known coatings as previously mentoned, and if a vtreous enamel coating is used the coefficient of expansion should be slightly less than that of the beryllia base.

I claim:

1. An electrical resstor comprising an insula'ting core of ceramic composition having a coeflicent of expansion between 5 to 10.5 10- inches per inch per degree centigrade, metal terminals mounted on said core having a coefiicient of expansion substantially equal to said core, and a helically formed elongated resistive element of titanium alloy including vanadium and aluminum on said core and in engagement With said metal terminals, said element having a cbefficient of expansion -of 9.5 t-o 10 10- inches per inch per degree centigrade.

2. An electrical resistor as set forth in claim 1 wherein the titanium metal alloy comprises 11% chrornium, 14% vanadium, 3.5 aluminum and the balance titanium.

3. An electrcal resistor as set forth in claim 1 wherein the titanium metal alloy comprises 4% vanadium, 6% aluminum and 90% titanium.

References Cited by the Examiner UNITED STATES PATENTS 2,318,4 5/1943 Stupakof l74--152.4 2,425,032 8/1947 Deyrup 338-352 2,691,088^ 10/1954 Ungewiss 338-302 2,696,544 12/1954 Poch 338-302 2,69 7,675 12/1954 Gaiser 338-309 X 2,804,409 8/-1957 Kessler et al 75-l75.5 X 2,864,697 12/1958 Busch et al. 75-1755 X 2,898,570 8/ 1959` Patrichi. 2,906,654 9/1959 Abkowitz 75-175.5 X 2,940,845 6/1960 Jaffee et al 75-175.5 X 3,147 ,ll5 9/1964 Vordahl 75-17S.5

FOREIGN PATENTS 579,735 8/ 1946 Great Britain. 7683051 2/1957 Great Britain.

RICHARD M. WOOD, Primary Exam'ner.

V. Y. MAYEWSKY, Assistant Exam'ner. 

1. AN ELECTRICAL RESISTOR COMPRISING AN INSULATING CORE OF CERAMIC COMPOSITION HAVING A COEFFICIENT OF EXPANSION BETWEEN 5 TO 10.5X10**-6 INCHES PER INCH PER DEGREE CENTIGRADE, METAL TERMINALS MOUNTED ON SAID CORE HAVING A COEFFICIENT OF EXPANSION SUBSTANTIALLY EQUAL TO SAID CORE, AND A HELICALLY FORMED ELONGATED RESISTIVE ELEMENT OF TITANIUM ALLOY INCLUDING VANADIUM AND ALUMINUM ON SAID CORE AND IN ENGAGEMENT WITH SAID METAL TERMINALS, SAID ELEMENT HAVING A COEFFICIENT OF EXPANSION OF 9.5 TO 10X10**-6 INCHES PER INCH PER DEGREE CENTIGRADE. 